Electric and electronic oven with a heated door structure



4 5, 1969 E L. E. FUSSELL ET AL 3,459,921

ELECTRIC AND ELECTRONIC OVEN WITH A HEATED DOOR STRUCTURE Filed Jan. 2. 1968 a Sheets-Shed 1 INVENTORS LYNN E. FUSSELL, ROBERT 0. oaaumv Aug. 5, 1969 FUSSELL ETAL 3,459,921

ELECTRIC AND ELECTRONIC OVEN WITH A HEATED DOOR STRUCTURE Filed Jan. 2, 1968 s Sheets-Sheet 2 g- 1969 E. FUSSELL ET AL 3,459,921

ELECTRIC AND ELECTRONIC OVEN WITH A HEATED DOOR STRUCTURE Filed Jan. 2', 1968 3 Sheets-Sheet 5 United States Patent 3,459,921 ELECTRIC AND ELECTRONIC OVEN WITH A HEATED DOOR STRUCTURE Lynn E. Fusscll, Richardson, Tex., and Robert D. Ogburn,

Louisville, Ky., assignors to General Electric Company,

a corporation of New York Filed Jan. 2, 1968, Ser. No. 694,956 Int. Cl. F27d 11/12 US. Cl. 219396 19 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a combination electric and electronic oven of the self-cleaning type including a metallic shell defining an oven cavity, means for supplying microwave energy to the oven cavity and resistive heating means in the oven cavity, control means for selecting either microwave heating or resistive heating, the shell having an opening therein providing access to the oven cavity and including an outwardly facing flange surrounding the opening, a coating of protective porcelain enamel on the inner surface of the shell and substantially covering the front surface of the outwardly facing flange, a metallic door for closing the opening, a continuous layer of electrically conductive ceramic carried by the porcelain enamel coating on the outwardly facing flange surrounding the opening and being in electrical connection with the metallic shell, the layer being chemically inert at elevated temperatures while retaining the electrically conductive properties thereof and generally matching the appearance of the porcelain enamel coating, a metallic gasket mounted on the metallic door and in electrical connection therewith and positioned to contact the conductive layer of enamel around substantially the entire perimeter of the opening, thereby to provide an electrically conductive panel constituting a short circuit for microwave energy from the metallic shell via the conductive layer and the metallic gasket to the metallic door.

The present invention relates to a combination electric and electronic oven of the self-cleaning type, and specifically to improved door constructions for such ovens.

It is an important object of the present invention to provide an electronic oven comprising a metallic shell defining an oven cavity adapted to be supplied with microwave energy, the shell having an opening therein providing access to the oven cavity and including an outwardly facing flange defining the opening, a coating of protective porcelain enamel on the inner surface of the shell and substantially covering the front surface of the outwardly facing flange, a metallic door for closing the opening, a continuous layer of electrically conductive ceramic carried by the porcelain enamel coating on the outwardly facing flange surrounding the opening and being in electrical connection with the metallic shell, the layer being chemically inert at elevated temperatures while retaining the electrically conductive properties thereof and generally matching the appearance of the porcelain enamel coating, and a metallic gasket mounted in the metallic door and in electrical connection therewith and positioned to contact the conductive layer around substantially the entire periphery of the opening, thereby to provide an electrically conductive path constituting a short circuit for microwave energy from the metallic shell via the conductive layer and the metallic gasket to the metallic door.

Another object of the invention is to provide an improved electronic oven of the type set forth wherein the conductive layer bonds to the shell in the same manner as does the porcelain enamel coating on the shell, the conductive layer and the porcelain enamel coating being 3,459,921 Patented Aug. 5, 1969 capable of being fired at the same firing temperature, thus to eliminate the necessity for an additional firing to apply the conductive layer.

Still another object of the invention is to provide an electronic oven of the type set forth wherein the conductive layer includes by weight from about 50% to about silver, from about 10% to 25% of a mixture of cobalt oxide and nickel oxide, and from about 10% to about 25% of chromium oxide and coloring matter, whereby after firing the silver is an integral part of a ceramic layer, thereby to protect the silver from abrasion and oxidation during use, all while retaining the good electrical conductivity of the silver to render the layer containing the silver electrically conductive.

Yet another object of the invention is to provide an improved electronic oven of the type set forth, wherein the metallic gasket is generally cylindrical in shape and is formed of a metal braid, the preferred metal being Monel metal, there also being disposed within the metal braid a batt of glass fibers to seal against gases.

A still further object of the invention is to provide a combination electric and electronic oven of the self-cleaning type comprising a metallic shell defining an oven cavity for carrying out bake and broil operations, means for supplying microwave energy to the oven cavity for carrying out microwave cooking operations therein, resistive heating means in the oven cavity for establishing bake and broil cooking conditions therein, control means selectively operable to control the microwave energy means and the resistive heating means to effect the desired cooking operation, the shell having an opening therein providing access to the oven cavity and including an outwardly facing flange defining the opening, a metallic door for closing the opening, gasket structure mounted between the shell and the door and substantially completely surrounding the opening, the gasket structure providing an electrically conductive path constituting a short circuit for microwave energy from the metallic seal to the metallic door when the control means is in position to operate the microwave energy means, temperature control means for the resistive heating means settable to control the resistive heating means when in a bake operation to hold selected baking temperatures within a bake temperature range, and cleaning means for the oven cavity including the control means settable to control the resistive heating means to supply heat energy to the oven cavity at a rate materially lower than the rate at which heat energy is supplied for baking operations to raise the temperature in the oven cavity to a degree where food soil lodged on the Walls thereof will be degraded and the oven will be self-cleaning, the gasket structure being chemically inert at the elevated temperatures encountered during self-cleaning of the oven while retaining the electrically conductive properties thereof.

Further features of the invention pertain to the particular arrangement of the parts and the particular composition thereof, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevational view, partly broken away and partly in section, of a household electronic range including therein a combination electric and electronic oven of the self-cleaning type and embodying the present invention;

FIG. 2 is a view similar to FIG. 1, but with the section taken at a diiierent point to illustrate the microwave heating system for the oven;

FIG. 3 is a fragmentary perspective view on a reduced scale of the upper forward portion of the range of FIG. 1 and illustrating specifically the door for closing the oven cavity therein;

FIG. 4 is a slightly enlarged view similar to FIG. 3 but showing the oven door in the open position thereof;

FIG. 5 is an enlarged fragmentary view in vertical section along the line 55 of FIG. 3;

FIG. 6 is still a further enlarged view of a portion of FIG. 5 and illustrating the details of construction of the gasket system forming a part of the door structure;

FIG. 7 is a further enlarged and diagrammatic view illustrating the conductive ceramic layer on the front flange surrounding the opening into the oven cavity; and

FIG. 8 is a diagrammatic representation of the control circuit for the range of FIGS. 1 and 2.

Referring to FIGS. 1 to 4, inclusive, of the drawings, there is illustrated a household electric range 10 embodying the features of the present invention, the range 10 including a combination electric and electronic oven of the self-cleaning type. More particularly, the range 10 comprises an upstanding substantially box-like metal body 11 carrying a substantially horizontal metal cooking top 12 and an upstanding metal backsplash 13 arranged at the rear of the cooking top 12. The body 11 constitutes a shell or casing and includes a front wall 14, an outer rear wall 15, and inner rear wall 16 spaced forwardly of the outer rear wall and defining a rear flue 17 therebetween, a pair of outer side walls 1 8 and a pair of inner side walls (not shown) respectively spaced inwardly of the inner side walls 18, a bottom wall 20 and a top wall 21, two channels 22 are arranged between each of the side wall pairs 18 and the associated inner side wall to provide a pair of upstanding side flues therewith. Also, the body 11 comprises a supporting base and bottom wall (not shown) positioned well below the bottom wall 20 and defining a lower machinery compartment 24 therebetween. The lower portion of the front wall 14 has an opening therein closed by a door 25 providing access to the lower machinery compartment 24.

The backsplash 13 is of hollow structure and includes a rear air inlet opening 26 in the top rear wall thereof and a communicating air outlet opening 27 in the bottom thereof, and similarly, the cooking top 12 is of hollow structure and includes an air passage 28 through the rear portion thereof and communicating between the air outlet opening 27 and the top of the rear flue 17. The bottom of the rear flue 17 communicates with the rear of the machinery compartment 24; and a fan or blower motor 29 is supported by the outer rear wall 15 within the rear top portion of the lower machinery compartment 24; which motor 29 is of the electric type provided with an operating shaft carrying a fan indicated at 30 in FIG. 1. The bottom ends of the side flues formed by the channels 22 communicate with the top side portions of the lower machinery compartment 24; the top end of the side flues formed by the channels 22 respectively communicate with four top flues 31, which four top flues 31 are respectively defined by transversely extending channel members 32 arranged between the top wall 21 and the cooking top 12, the top flues 31 communicating with the interior of the cooking top 12. The cooking top 12 has a number of openings (ordinarily four) therein, in which a corresponding number of surface heating units 33 are removably arranged.

In view of the foregoing, it will be understood that when the electric motor 29 is operated, the fan 30 draws ambient air into the air inlet opening 26, this air passing downwardly through the backsplash 13 and thence through the openings 27 and 28 into the rear of the lower machinery compartment 24. The air in the machinery compartment 24 is then circulated upwardly through the side flues and thence inwardly through the top flues 31 and below the cooking top 12, whereby the air escapes from below the cooking top 12 through the 4 surface heating units 33 back to the exterior. This circulation of air through the rear flue 17, the side flues and the top flues 31 is employed for a cooling purpose during the heat-cleaning operation.

A substantially box-like metal liner or shell 40' is housed in the upper portion of the body 11, which shell 40- defines an oven cooking cavity 41 therein; and which shell 40 includes a rear wall 42, a top wall 43, a bottom wall 44 and a pair of side walls 45. The interior surfaces of the shell 40 carry a layer 46 of porcelain enamel of the glass frit type (see FIGS. '6 and 7). The forward edges of the top wall 43, the bottom wall 44 and the side walls 45 define an opening into the cooking cavity 41, there being a continuous outwardly facing flange 47 which is bent back upon itself on the rear surface thereof as at 48, the porcelain enamel layer 46 extending out onto the front surface of the outwardly facing flange 47 and terminating at the outer edge thereof for a purpose to be described more fully hereinafter. The front wall 14 has an opening therein slightly greater than the area defined by the outer edges of the flange 47 and has a rearwardly directed flange 49 which is suitably secured to the several walls 43, 44 and 45, as by welding, thus to interconnect the front wall 14 and the oven shell 40.

The shell top wall 43 is spaced well below the cabinet top wall 21 and is heat-insulated therefrom by a batt 51 of fibrous glass arranged in compression therebetween. The shell bottom wall 44 is spaced well above the cabinet bottom wall 20 and is heat-insulated therefrom by a batt 52 of fibrous glass arranged in compression therebetween; the shell rear wall 42 is spaced well forwardly of the casing rear wall 16 and is heat-insulated therefrom by a batt 53 of fibrous glass arranged in compression therebetween; and the shell side walls 45 are respectively spaced well inwardly of the casing inner side walls and are respectively heat-insulated therefrom by a pair of batts of fibrous glass respectively arranged in compression therebetween. It will be understood that the several 'batts described respectively engage against the associated walls of the shell 40 and forwardly to the forward end thereof and specifically to the flange 49 (see FIG. 6), as well as the adjacent portions of the wall 14 surrounding the opening thereinto; whereby the shell 40 is exceedingly well heat-insulated. In the structure of the heat insulation, the batts 51, 52 and 53 and those disposed between the side walls 19 and 45 may be formed either separate from each other or in part integral with each other in accordance with conventional practice in the heat-insulating of the oven shell 40, whereby the individual references to the several batts has been made only in the interest of a definite description of the locations thereof.

An upper or broil electric heating unit 61 is removably arranged in the upper portion of the oven cavity 41 adjacent to the shell top wall 43, a lower or bake electric heating unit 62 is removably arranged in the lower portion of the oven cavity 41 adjacent to the shell bottom wall 44; and a substantially loop-like electric heating unit 63 is arranged in surrounding relation with the exterior front portion of the shell 40 immediately rearwardly of the surrounding front flange 47 carried thereby, the heating unit 63 being therefore arranged around the periph' cry of the opening of the oven cavity 41 and being disposed within the space defined by the forward portions of the walls of the shell 40, the portion 48 of the flange 47 and the flange 49 on the front wall 14 (see FIG. 6). It will 'be understood there also may be provided an oven lamp for the purpose of illuminating the interior of the oven cavity 41 in a conventional manner, and the shell 40 may carry the usual tiers of horizontally aligned shell supporting bosses, which structures have not been illustrated in the interest of clarity.

As is shown in FIG. 1 of the drawing, an oxidizing unit is embedded in the top batt 51; which unit 70 is preferably of the construction and arrangement of that disclosed in U.S. Patent No. 2,900,483, granted on Aug.

18, 1959 to Stanley B. Welch. The unit 70 is employed to dispose of and to burn fumes generated within the oven cavity 41 during the cooking operation and during the heat-cleaning operation thereof, the unit 70 essentially comprising a casing 71 constituting a flue communicating between the top of the oven cavity 41 and the space below one of the surface heating units 33 carried by the cooking top 72. Housed within the casing 71 is an electric heating element 72 and a wire screen 73 that is coated with a catalytic metal, such, for example, as platinum, that is specially adapted to promote the oxidation of carbon and carbon compounds so as to eliminate smoke, carbon monoxide and other objectionable products exhausted from the oven cavity 41. The outlet from the top of the casing 71 of the unit 7%) communicates with a flue 74 defined by a channel 75 and communicating with a stack 76 terminating below one of the rear surface heating units 33, as best shown in FIG. 1.

Further, the range comprises a front door 80 that is mounted on the front of the body 11 'by hinge structure (not shown), and movable about the lower edge thereof between a substantially horizontal open position as illustrated in FIG. 4 and a substantially vertical closed position with respect to the open front of the oven cavity 41 as illustrated in FIGS. 1 to 3. When the front door 80 occupies its closed position, as shown in FIG. 1, the top edge thereof is positioned below the front end of the cooking top 12 and the bottom edge thereof is positioned above the top of the door 25. Moreover, the outer edge of the cooking top 12, the front or outer wall of the front door 80 and the front or outer wall of the door 25 are arranged in vertically aligned or flush condition so as to lend a finished appearance to the front of the range 10.

The front door 80 more particularly includes a metal outer sheet 82 (see FIG. 5 a metal inner sheet 83 spaced well inwardly of the outer sheet 82, and a metal intermediate sheet 84 disposed between the outer sheet 82 and the inner sheet 83. The outer sheet 82 carries an inturned flange 85 around the periphery thereof, the flange 85 extending inwardly toward and to a point spaced a short distance from the front wall 14 when the door 80 is in its closed position. The outer sheet 82 also carries a handle 86 adjacent to the upper edge thereof for use in moving the door 80 between its closed and open positions. The intermediate sheet 84 has a forwardly directed flange 87 that carries an outwardly directed flange 88 extending therearound, the flange 88 in turn carrying a forwardly directed flange 89 that lies inside of the flange 85 and extend completely therearound and is suitably secured thereto as by welding. A movable sheet 90 is positioned within the door 80 immediately behind the sheet 82 and there is provided a plurality of springs 91 which urge the sheet 90 toward a pair of batts 92 of fibrous glass used for heat insulation purposes. As illustrated, the flange 87 is dis posed substantially parallel to and spaced a short distance from a portion of the flange 49. Finally, it is pointed out that the inner sheet 83 has a forwardly directed flange 93 around the periphery thereof extending toward the intermediate sheet 84, a batt 94 of fibrous glass being disposed between the sheets 83 and 84, suitable structure, not shown, being provided to interconnect these parts.

Referring to FIG. 2 of the drawings there is illustrated in the lower machinery compartment 24 a microwave generator 65 which is useful in generating microwave energy that is supplied to the cooking cavity 41 for carrying out microwave cooking operations therein. More specifically, the output of the microwave generator 65 isconnected as the input to a transmission line 66 which extends rearwardly from the lower machinery compartment 24 into the flue space 17 behind the inner rear wall 16 and then upwardly and inwardly through the inner rear wall 16 and through the rear wall 42 of the shell 40 where it connects to an antenna 67. The antenna 67 is spaced a short distance below the top wall 43 and below the upper electric heating unit 61 and generally centraly in a lateral direction along the rear wall 42. During the microwave cooking operation, it is also desirable to move the food within the cooking cavity 41, and to this end a rotating food support 69 is provided in the bottom of the cooking cavity 41, but spaced upwardly from the bottom wall 44 and the lower electric cooking unit 62. A drive motor 68 is mounted in the lower machinery compartment 24 and has the output thereof connected to the support 69 to effect rotation thereof.

During the use of the range 10, and particularly during use of the oven therein, it is desirable from time to time to carry out any one of several operations within the oven cavity 41, and more particularly, it is desirable to carry out normal bake operations, normal broil operations, microwave cooking operations and heat-cleaning operations. There is diagrammatically illustrated in FIG. 8 of the drawings circuitry for selectively effecting the several types of operations within the cooking cavity 41. As illustrated, a 230 volt, 60 cycle, A.C. source is provided including a conductor 95 and a grounded conductor N. The conductor 95 is connected to a switch 96 including a movable contact 97, the contact 97 being movable into an upper position whereby to connect the conductor 95 to a conductor 98 and also being movable to a lower position whereby to connect the conductor 95 to a conductor 99. The conductor 98 is connected as the input to the microwave generator 65, the output from the microwave generator 61 being connected by the transmission line 66 to the antenna 67 disposed within the oven shell 40. The conductor 99 is connected as an input to the controller 55 which includes a movable member 56 that may be placed in any one of three positions, namely, into connection with a contact 57 to effect a bake operation, or into connection with the contact 58 to effect a broil operation, or into connection with the contact 59 to effect a heat-cleaning operation. It will be understood that the contacts 57, 58 and 59 are effective to place the several heating units 61, 62 and 63 in appropriate connection to carry out the desired operation. It will also be understood that the controls for the switch 96 and the controller 55 are positioned on the backsplash 13, see FIGS. 1 and 2.

The details of the manner in which the circuit of FIG. 8 may be utilized to carry out bake, broil and heat cleaning operations are set forth in US. Patent No. 3,121,158 granted Feb. 11, 1964 to Bohdan Hurko, it simply being pointed out here that in the heat-cleaning operation the temperature within the heating cavity 41 is elevated into the range from about 750 F. to about 950 F. to effect the cleaning operation. As a result, all of the parts associated with the oven are heated to corresponding temperatures, whereby all parts in thermal contact therewith must be able to withstand such temperatures. To effect heat-cleaning, the controller 55 and the switch 96 are set to control the several resistive heating units 61, 62 and 63 to supply heat energy to the oven cavity 41 at a rate materially lower than the rate at which heat energy is supplied for baking operations to raise the temperature of the oven cavity 41 into the range indicated, whereby food soil lodged on the walls of the shell 40 will be degraded and the walls cleaned.

It is highly desirable when carrying out cooking and heat-cleaning operations within the oven cavity 41 that there be a good mechanical seal between the periphery of the door and the flange 47 around the front of the cooking cavity 41. It is further desirable during the carrying out of a microwave cooking operation within the cooking cavity 41 that there be a good electrical connection between the metallic portions of the door 80 and the metallic portions of the oven shell 40 so as to provide an electrically conductive path constituting a short circuit for microwave energy from the metallic shell 40 to the metallic door 80. To this end the improved gasket structure of the present invention has been provided, the details of the construction thereof being best set forth in FIGS. 5, 6 and 7 of the drawings.

Referring first to FIGS. and 6, there is illustrated a gasket structure 100 which provides a seal and an electrical connection between the outer surface of the oven shell 40 and the inner surface of the oven door 80, and specifically between the outwardly facing flange 47 on the oven shell 40 and the intermediate sheet 84 on the door 80. It will be understood that the gasket structure 100 includes a compressible gasket 101 and extends substantially completely around the opening into the oven cavity 41, reference being made to FIG. 4 wherein it will be seen that the flange 47 extends completely around the periphery of the opening into the cooking cavity, while the gasket 101 mounted on the door 80 also extends completely around the exposed surface of the intermediate sheet 84 and in position to contact the flange 47 when the door 80 is in the closed position as illustrated in FIGS. 5 and 6. The gasket 101 is more particularly formed of a generally cylindrical length of metal braid, the length of metal braid being such that it extends around and has a length equal to that of the flange 47, the metal braid being deformable and collapsible to permit bending at the corners and to permit deformation thereof to the cross-sectional shape illustrated in FIG. 6. Preferably, the metal braid forming the gasket 101 is made of a metal that is heat resistant and capable of withstanding high temperatures without corrosion or degrading thereof, the preferred metal being Monel metal. This characteristic of the metal braid forming the gasket 101 is particularly important during the heat-cleaning operation, since the perimeter heater 63 is energized during the heat-cleaning operation and maintains a high temperature, such as in the range 750 F. to 950 F., at the gasket 101.

It is also desirable that the gasket 101 serve as a seal against the escape of gases during the cooking and heatcleaning operations. To this end, a batt 102 of glass fibers is disposed within the generally cylindrical braided gasket 101 and extends the entire length thereof, it being noted that the batt 102 is also readily deformable as illustrated in FIG. 6 to conform to the shape assumed by the gasket 101.

Structure is provided for mounting the gasket 101 upon the door 80, part of the mounting structure being a mounting bracket 103 formed of metal and having a mounting flange 104 thereon which is suitably secured, as by welding, to the flange 93 on the inner sheet 83. The lower or inner edge of the mounting bracket 103 carries an inner flange 105 disposed substantially normal thereto. A second part of the mounting structure is a metal clamping bracket 106 which is disposed substantially parallel to the mounting bracket 103 and includes an inner flange 107 normal to the bracket 106 and disposed parallel to the inner flange 105, the outer edge of the clamping bracket 106 carrying a clamping flange 108 thereon. Aligned openings are provided in the brackets 103 and 106, the opening in the bracket 103 being threaded so that the openings may receive therethrough the shank of a bolt 109, the threads on the bolt 109 engaging the threaded opening in the bracket 103. As the bolt 109 is threaded home, the inner flange 107 contacts the mounting bracket 103 and thereafter continued tightening of the bracket 109 serves to move the clamping flange 108 toward the mounting flange 104 to clamp the several parts therebetween.

There further is provided a shim 110 disposed between the gasket 101 and the inter-mediate sheet 84, the shim 110 including a rearwardly directed flange 111 which overlies the clamping flange 108. It will be appreciated that tightening of the bolt 109 Will therefore cause the clamping flange 108 to press the flange 111 against the associated portion of the gasket 102 and to clamp the associated portion of the gasket 102 against the mounting bracket 103. The free portion of the gasket 101 extends radially outwardly from the flange 93 and is backed by the shim and is disposed opposite the shell flange 47. The mounting structure described places the metal gasket 101 in good electrical contact with the metallic portions of the door 80, and more particularly with the several sheets 83 and 84 thereof, this good electrical contact being around the entire periphery of the door 80.

During the carrying out of the microwave cooking operation in the oven shell 40, it is essential for safety purposes that there be no path for propagation of microwave energy from the range 10, and specifically through the juncture between the oven shell 40 and the oven door 80. More specifically, it is necessary that the gasket structure 100 provide an electrically conductive path constituting a short circuit for microwave energy from the metallic shell 40 to the metallic portions of the door 80. In the prior art ovens, the porcelain coating 46 has extended from the interior of the oven, such as along the wall 43 in FIG. 7, and out along the flange 47 and around the outer end thereof. Since it is the front face (the face disposed to the right in FIGS. 6 and 7) of the flange 47 which in in physical contact with the door 80, it is necessary that this surface be electrically conductive if an electrical connection is to be made with the metal braid gasket 101. In accordance with the present invention, this forward face of the flange 47 is rendered conductive by applying over the porcelain coating 46 a continuous layer 120 of electrically conductive ceramic, the layer 120 being in good electrical connection with the oven shell 40 via the flange 47 and the bent back portion 48 thereof.

In manufacturing the oven shell 40, the porcelain coating 46 is applied and given the first firing in the usual manner. Thereafter the outer edge of the flange 47 is ground as at 115 in FIG. 7 to remove all of the porcelain 46 therefrom whereby to leave the edge 115 completely free and clean of porcelain, and also to leave clean the rear surface of the flange portion 48. A ceramic slip is then prepared having the following formulation.

Ingredient: Percent by weight Silver powder 50 Ground coat enamel frit 25 Semi-opaque enamel frit 25 The ingredients are then thoroughly mixed in an organic vehicle of the usual type utilized in forming ceramic slips and in then applied by painting to the front surface of the flange 47 over the porcelain coating 46 thereon and also over the exposed edge 115 and the exposed rear surface of the flange portion 48. The oven liner is then given the usual final firing which serves to final fire the porcelain coating 46 and to fire the conductive layer simultaneously, whereby no separate and additional firing is required to apply the conductive layer 120. After the firing operation, the finished conductive layer 120 completely covers the forward face of the flange 47 as at 121, and specifically the porcelain coating 46 thereon, and extends inwardly as at 122 into the oven and also outwardly a at 123 across the exposed surface 115 to make good electrical contact therewith and then along the rear of the flange portion 48 also to make good electrical contact therewith as at 124, the layer 120 typically having a Width of /s" and a thickness of about 0.002".

The layer 120 is highly conductive electrically, whereby when the oven door 80 is in its closed position, a good electrical contact is provided from the door sheets 83-84 to the metal braid of the gasket 101 and through the conductive layer 120, and specifically the portions 123 and 124 thereof to the flanges 4748, and thus to the oven Shell 40. As a result, the area between the front of the oven shell 40 and the oven door 80 is closed by the gasket structure 100 providing both a seal against gases and an electrical conductive path constituting a short-circuit for microwave energy. When formed from the formulation as set forth above, the conductive layer 120 has the same color and appearance as the porcelain coating 46, whereby the presence of the conductive layer 120 is not noticeable. Furthermore, the conductive properties and the desirable appearance of the conductive layer 120 are maintained even after prolonged usage, wherein the layer is abraded by the metal braid 101 and after prolonged heating at elevated temperatures including the high temperatures utilized in heat-cleaning, and specifically the temperatures generated by the periphery heater 63 disposed adjacent thereto.

In the formulation set forth above, the powdered silver prov-ides the necessary conductivity of the layer 120, the preferred powdered silver being that sold under the designation Silpowder 130, which product has a particle size in the range from about 0.6 to about 3.0 microns. It is desirable to utilize at least 50 parts by weight of this silver powder in the formulation and as much as about 75 parts by weight of silver may be used.

The ground coat enamel first provides good adherence, particularly to the bare metal areas as at the portions 123 and 124. The ground coat enamel frit is formulated from cobalt oxides and nickel oxides, these oxides giving a color to the fired conductive layer 120 that closely matches that of the porcelain coating 40 over which it is applied. As little as 10% by weight of the ground coat enamel frit may be utilized and as much as 25% by weight may be utilized and still produce a useful conductive layer 120. Selection of the proper ground coat enamel frit allows the formulation to be fired at the same firing schedule as the porcelain coating 46, the frits in the conductive layer 120 having a viscosity similar to those used in the porcelain coating 46.

The semi-opaque enamel frit in the formulation is essentially chromium oxide and certain coloring oxides, if desired, so as to match more closely the color of the porcelain coating 46. The semi-opaque enamel frit may comprises as little as 10% by weight of the formulation and as much as 25 by Weight of the formulation if a semi-glossy or glossy surface on the fired conductive layer 120 is to be maintained.

Instead of being applied as a paint, the ingredients of the formulation may be applied to a transfer tape and then applied to the oven shell 40 at the flange 47 from the transfer tape. In this connection, it is desirable that the slip of the porcelain coating 46 be wiped from the surfaces 115 on the flanges 46-58 and from the rear of the flange 48 prior to firing, these surfaces being oxidized during the enamel firing of the coating 46, whereby the oxide must be removed by grinding or filing to present clean metal surfaces for the slip of the conductive layer 120.

Summarizing the characteristics of the conductive layer 120 and the advantages thereof, the material of the layer 120 bonds to the porcelain coating 46 and the bare metal surfaces as at 115 and the rear of the flange 48 in a highly satisfactory and desirable manner. In fact, the ingredients of the layer 120 can be applied to the oven shell 40 just as a porcelain enamel and can be fired during the same firing as the porcelain coating 46, whereby a subsequent oven firing for the layer 120 is not needed. The fired conductive layer 120 has the same appearance as the porcelain coating 46, i.e., the layer matches in appearance the interior of the oven shell 40 and is attractive in appearance. Since the powdered silver in the conductive layer 120 is an integral part of the layer, the silver is protected from abrasion and oxidation during the baking or roasting of food in the oven, it being pointed out that ordinary metallic silver is very susceptible to sulphur fumes which quickly discolor it. Apparently, the ceramic portions of the layer 120 protect the metallic silver from such chemical damage and also from mechanical damage due to abrasive contact with the metal braid forming the gasket 101. All of these advantages are obtained while providing a good electrical conductivity in the layer 120. Finally, and of particular importance when the oven is of the 10 self-cleaning type, the extremely high temperatures encountered during heat-cleaning operation, these temperatures being of the order of 750 F. to- 950 F., does not discolor or age the conductive layer 120'.

Recapitulating, the gasket structure 100 provides both a good gas seal between the oven shell 40 and the oven door during all cooking and cleaning operations within the oven shell 40, and also provides a good electrical contact between the oven shell 40 and the oven door 80, which electrical contact is essential during microwave cooking operation within the oven shell 40. More specifically, the use of the batt 102 of glass fibers within the metal braid gasket 101 provides the necessary seal against the passage of gases that may be formed and tend to escape during the cooking operations and the heat-cleanmg operation. These gases instead are directed upwardly and outwardly through the unit 70 where any objectionable components thereof are destroyed by oxidative action. The gasket structure during the microwave cookmg operation in the oven shell 40 provides an electrically conductive path constituting a short circuit for microwave energy from the metallic oven shell 40 the metallic portions of the oven door 80. This electrically conductive path can be traced from the metal shell 40 through the outwardly facing flange 47 and through the layer portions 123-124 onto the main forward layer portion 121 of the conductive layer 120. The metal braid gasket 101 bears against the outer surface of the conductive layer as at 121 and is in good electrical contact therewith. The metal braid gasket 101 is in good electrical contact with the several metallic portions of the oven door 80 including the sheets 83 and 84. Accordingly, it will be seen that there is a continuous path of substantial current carrying capacity between the metallic oven liner 40' and the metallic portions of the oven door 80, whereby to provide a short circuit for microwave energy and thus to prevent the escape of microwave energy from the oven through the juncture between the forward portion of the oven and the oven door 80.

During the heat-cleaning operation of the range 10, the temperature Within the cooking cavity 41 is slowly raised to a temperature within the range from about 750 and 950 F., and the perimeter heating unit 63 is en erglzed, thereby to provide a temperature at least in this range immediately behind the forward facing flange 47. As a consequence, the conductive layer 120 is raised to such elevated temperatures, as also is the metallic braid gasket 101. It therefore is essential that these parts be capable of withstanding such temperatures and still retain the gasket properties thereof and the electrical conduct1vity properties thereof as well as a good visual appearance. The Monel metal from which the braid of the gasket 101 is formed readily withstands such temperatures and still retains its flexibility, electrical conductivity and pleasing appearance. It further has been found that the conductive layer 120 likewise retains its electrical conduct1vity properties after repeated heatings to such temperatures, all without discoloring or marring the visual appearance thereof.

It will be seen that there has been provided a door structure for a combination electric and electronic oven of the self-cleaning type, and specifically a gasket structure therefor, which fulfills all of the objects and advantages set forth above.

While there has been described what is at present consideration to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the ap pended claims all such modifications as well within the true spirit and scope of the invention.

What is claimed is:

1. An electronic oven comprising a metallic shell defining an oven cavity adapted to be supplied with microwave energy, said shell having an opening therein providing access to said oven cavity and including an outwardly facing flange defining said opening, a coating of protective porcelain enamel on the inner surface of said shell and substantially covering the front surface of said outwardly facing flange, a metallic door for closing said opening, a continuous layer of electrically conductive ceramic carried by said porcelain enamel coating on said outwardly facing flange surrounding said opening and being in electrical connection with said metallic shell, said layer being chemically inert at elevated temperatures while retaining the electrically conductive properties thereof and generally matching the appearance of said protective coating, and a metallic gasket mounted on said metallic door and in electrical connection therewith and positioned to contact said conductive layer around substantially the entire perimeter of said opening, thereby to provide an electrically conductive path constituting a short circuit for microwave energy from said metallic shell via said conductive layer and said metallic gasket to said metallic door.

2. The electronic oven set forth in claim 1, wherein said layer of electrically conductive ceramic contains from about 50% by weight to about 75% by weight powdered silver.

3. The electronic oven set forth in claim 1, wherein said layer of electrically conductive ceramic contains by weight from about 50% to about 75 silver, from about to about 25% of a mixture of cobalt oxide and nickel oxide, and from about 10% to about 25 of chromium oxide and coloring materials.

4. The electronic oven set forth in claim 1, wherein, said layer of electrically conductive ceramic is in electrically conductive contact with said shell on the outer edge of said flange and on the rear surface thereof.

5. The electronic oven set forth in claim 1, wherein said layer of electrically conductive ceramic has a width of about inch on the outwardly facing surface of said flange and a thickness of about 0.002 inch.

6. The electronic oven set forth in claim 1, wherein said metallic gasket is a generally cylindrical length of metal braid.

7. The electronic oven set forth in claim 6, wherein said metallic braid is formed of Monel metal.

8. The electronic oven set forth in claim 6, wherein a batt of glass fibers is disposed in said generally cylindrical length of metal braid to seal said metal braid against the passage of gases therethrough.

9. An electronic oven comprising a metallic shell de fining an oven cavity adapted to be supplied with microwave energy, said shell having an opening therein providing access to said oven cavity and including an outwardly facing flange defining said opening, a heating unit mounted on said shell adjacent to the rear surface of said outwardly facing flange and extending substantially around said opening, a coating of protective porcelain enamel on the inner surface of said shell and substantially covering the front surface of said outwardly facing flange, a metallic door for closing said opening, a continuous layer of electrically conductive ceramic carried by said porcelain enamel coating on said outwardly facing flange surrounding said opening and being in electrical connection with said metallic shell adjacent to said heating unit, said layer being chemically inert at elevated temperatures resulting from the operation of said heating unit while retaining the electrical conductive properties thereof and generally matching the appearance of said protective coating, and a metallic gasket mounted on said metallic door and in electrical connection therewith and positioned to contact said conductive layer around substantially the entire perimeter of said opening, thereby to provide an electrically conductive path constituting a short circuit for microwave energy from said metallic shell via said conductive layer and said metallic gasket to said metallic door.

10. A combination electric and electronic oven of the self-cleaning type comprising a metallic shell defining an oven cavity for carrying out bake and broil operations,

means for supplying microwave energy to said oven cavity for carrying out microwave cooking operations therein, resistive heating means in said oven cavity for establishing bake and broil cooking conditions therein, control means selectively operable to control said microwave energy means and said resistive heating means to effect the desired cooking operation, said shell having an opening therein providing access to said oven cavity, a metallic door for closing said opening, gasket structure mounted between said shell and said door and substantially completely surrounding said opening, said gasket structure providing an electrically conductive path constituting a short circuit for microwave energy from said metallic shell to said metallic door when said control means is in position to operate said microwave energy means, temperature control means for said resistive heating means settable to control the resistive heating means when in a bake operation to hold selected baking temperatures within a baking temperature range, and cleaning means for said oven cavity including said control means settable to control said resistive heating means to supply heat energy to said oven cavity at a rate materially lower than the rate at which heat energy is supplied for baking operations to raise the temperature in the oven cavity to a degree where food soil lodged on the walls thereof will be degraded and the oven will be selfcleaning, said gasket structure being chemically inert at the elevated temperatures encountered during self-cleaning of said oven while retaining the electrically conductive properties thereof.

11. The combination set forth in claim 10, wherein said gasket structure is compressible between said shell and said door to ensure a good electrical contact therebetween.

12. The combination set forth in claim 10, wherein said gasket structure has incorporated therein means providing a good seal between said shell and said door to prevent the escape of gases therebetween.

13. A combination electric and electronic oven of the self-cleaning type comprising a metallic shell defining an oven cavity for carrying out bake and broil operations, means for supplying microwave energy to said oven cavity for carrying out microwave operations therein, resistive heating means in said oven cavity for establishing bake and broil cooking conditions therein, control means selectively operable to control said microwave energy means and said resistive heating means to effect the desired cooking operation, said shell having an opening therein providing access to said oven cavity and including an outwardly facing flange defining said opening, a perimeter heating unit mounted on said shell adjacent to the rear surface of said outwardly facing flange and extending substantially around said opening, a metallic door for closing said opening, gasket structure mounted between said shell and said door and substantially completely surrounding said opening, said gasket structure providing an electrically conductive path constituting a short circuit for microwave energy from said metallic shell to said metallic door when said control means is in position to operate said microwave energy means, temperature control means for said resistive heating means settable to control the resistive heating means when in a bake operation to hold selected baking temperatures within a baking temperature range, and cleaning means for said oven cavity including said control means settable to control said resistive heating means and said perimeter heating unit to supply heat energy to said oven cavity at a rate materially lower than the rate at which heat energy is supplied for baking operations to raise the temperature in the oven cavity to a degree where food soil lodged on the walls thereof will be degraded and the oven will be self-cleaning, said gasket structure being chemically inert at the ele vated temperatures encountered during self-cleaning of said oven while retaining the electrically conductive properties thereof.

14. A combination electric and electronic oven of the self-cleaning type comprising a metallic shell defining an oven cavity for carrying out bake and broil operations, means for supplying microwave energy to said oven cavity for carrying out microwave cooking operations therein, resistive heating means in said oven cavity for establishing bake and broil cooking conditions therein, control means selectively operable to control said microwave energy means and said resistive heating means to effect the desired cooking operation, said shell having an opening therein providing access to said oven cavity and including an outwardly facing flange defining said opening, a coating of protective porcelain enamel on the inner surface of said shell and substantially covering the front surface of said outwardly facing flange, a metallic door for closing said opening, a continuous layer of electrically conductive ceramic carried by said porcelain enamel coating on said outwardly facing flange and being in electrical connection with said metallic shell, said layer generally matching the appearance of said protective coating, a metallic gasket mounted on said metallic door and in electrical connection therewith and positioned to contact said conductive layer around substantially the entire perimeter of said opening, said layer and said metallic gasket providing an electrically conductive path constituting a short circuit for microwave energy from said metallic shell to said metallic door when said control means is in position to operate said microwave energy means, temperature control means for said resistive heating means settable to control the resistive heating means when in a bake operation to hold selected baking temperatures within a baking temperature range, and cleaning means for said oven cavity including said control means settable to control said resistive heating means to supply heat energy to said oven cavity at a rate materially lower than the rate at which heat energy is supplied for baking operations to raise the temperature in the oven cavity to a degree where food soil lodged on the walls thereof will be degraded and the oven will be self-cleaning, said layer and said metallic gasket being chemically inert at the elevated temperatures encountered during self-cleaning of said oven while retaining the electrically conductive properties thereof.

15. The combination electric and electronic oven set forth in claim .14, wherein said layer of electrically conductive ceramic contains from about by Weight to about by weight powdered silver.

16. The combination electric and electronic oven set forth in claim 14, wherein said layer of electrically conductive ceramic contains by Weight from about 50% to about 75% powdered silver, from about 10% to about 25% of a mixture of cobalt oxide and nickel oxide, and from about 10% to about 25 of chromium oxide and coloring materials.

17. The combination electric and electronic oven set forth in claim 14, wherein said metallic gasket is a generally cylindrical length of metal braid.

18. The combination electric and electronic oven set forth in claim 17, wherein said metallic braid is formed of Monel metal.

19. The combination electric and electronic oven set forth in claim 17, wherein a batt of glass fibers is disposed in said generally cylindrical length of metal braid to seal said metal braid against the passage of gases therethrough.

References Cited UNITED STATES PATENTS 3,121,158 2/1964 Hurko 219-397 3,270,183 8/1966- Jordan 219-398 3,327,094 6/1967 Martin et al. 2l9----393 VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R. 

